1. Field of the Invention
The present invention relates to a commutator of an electric motor for use with a power driven tool, etc. and a method of manufacturing the same.
2. Description of the Prior Art
In a commutator of an electric motor, it is proposed to provide means for preventing commutator segments from shifting. As disclosed in U.S. Pat. Nos. 2,533,775, 3,290,527 and 3,450,914, such means conventionally include metal rings which are embedded within a hub made of synthetic resin and which are disposed within recesses formed by anchoring portions of the commutator segments.
However, such metal rings require not to be in contact with commutator segments and therefore, it is difficult to manufacture the commutator. Further, since the synthetic resin exists between the metal rings and the commutator segments, the metal rings do not effectively prevent the commutator segments from shifting. Additionally, the metal rings tend to be broken under high temperature caused by commutation sparks.
Japanese Laid-Open Utility Model Publication No. 60-82967 discloses a ring made of ceramic which is embedded within a hub made of synthetic resin and which is positioned within recesses formed by anchoring portions of commutator segments in contacting relationship therewith. Japanese Laid-Open Patent Publication No. 61-98139 discloses a ceramic ring formed integrally with commutator segments.
However, in the former Japanese prior art construction, the ceramic rings tend to be easily broken and to have uneven sizes because of its material and configuration. Therefore, it has been very difficult to assemble the ceramic rings and to thereafter form the hub by injecting synthetic resin thereto. Further, in the latter Japanese prior art construction, the ceramic ring tends to shrink after molding with commutator segments. Therefore, the commutator tends to be easily broken and to have uneven sizes. For this reason, this construction has not been practically employed.